Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device and a manufacturing method thereof are provided. The semiconductor device includes first and second epitaxial layers, and first and second semiconductor layers. The second epitaxial layer is disposed on the first epitaxial layer. The first semiconductor layer extends from above the second epitaxial layer to a top surface of the second epitaxial layer. A vertically extending region of the first semiconductor layer has a body portion and an extending portion extending from a bottom end of the body portion to the second epitaxial layer. A width of the body portion is greater than a width of the extending portion. The second semiconductor layer is disposed on the second epitaxial layer, and laterally surrounds the vertically extending region of the first semiconductor layer. A portion of the second semiconductor layer extends between and overlaps with the body portion of the first semiconductor layer and the second epitaxial layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 109108160, filed on Mar. 12, 2020. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND Technical Field

The present disclosure relates to a semiconductor device and amanufacturing method thereof, and particularly, to a heterojunctionbipolar transistor (HBT) device and a manufacturing method thereof.

Description of Related Art

A bipolar junction transistor (BJT) is a semiconductor device with threeterminals. As compared to a single polarity transistor (e.g., a fieldeffect transistor), the BJT is conducted by both of electrons and holes,thus available in either polarity. The BJT can be functioned as a signalamplifier, and has advantages including great control of power, highoperation speed, great durability and so forth.

A heterojunction bipolar transistor (HBT) is a type of the BJT. Emitterand base terminals of HBT are made of different materials, thus aheterojunction is formed between the emitter terminal and the baseterminal. As compared to a homogeneous BJT, the HBT can be utilizedunder higher frequency. Therefore, the HBT can be applied incommunication devices, high speed circuits or so forth.

SUMMARY

A HBT device with increased operation frequency and a manufacturingmethod of such HBT device are provided.

An aspect of the present disclosure provides a semiconductor device. Thesemiconductor device comprises: a first epitaxial layer, having a firstconductive type; a second epitaxial layer, disposed on the firstepitaxial layer, and having a second conductive type complementary tothe first conductive type; a first semiconductor layer, extending fromabove the second epitaxial layer to a top surface of the secondepitaxial layer, and having the first conductive type, wherein avertically extending region of the first semiconductor layer has a bodyportion and an extending portion below the body portion and extendingfrom a bottom end of the body portion to the second epitaxial layer, anda width of the body portion is greater than a width of the extendingportion; and a second semiconductor layer, disposed on the secondepitaxial layer and laterally surrounding the vertically extendingregion of the first semiconductor layer, wherein a portion of the secondsemiconductor layer extends between the body portion of the firstsemiconductor layer and the second epitaxial layer, and is overlappedwith the body portion of the first semiconductor layer and the secondepitaxial layer along a vertical direction.

In some embodiments, the portion of the second semiconductor layer islaterally spaced apart from the extending portion of the firstsemiconductor layer.

In some embodiments, the portion of the second semiconductor layer is inlateral contact with the extending portion of the first semiconductorlayer through a pad pattern.

In some embodiments, the semiconductor device further comprises: aninsulating layer, extending between the body portion of the firstsemiconductor layer and the second semiconductor layer, and between thebody portion of the first semiconductor layer and the pad pattern.

In some embodiments, the first semiconductor layer further has alaterally extending region, the vertically extending region is locatedbelow the laterally extending region and extending downwardly from abottom end of the laterally extending region, and the laterallyextending region is spaced apart from the second semiconductor layeralong a vertical direction.

In some embodiments, the laterally extending region of the firstsemiconductor layer is in contact with the second semiconductor layerthrough a dielectric layer.

Another aspect of the present disclosure provides a manufacturing methodof a semiconductor device. The method comprises: sequentially forming afirst epitaxial layer and a second epitaxial layer on a substrate;forming a pad pattern and a mask pattern on the second epitaxial layer,wherein the pad pattern is located between the second epitaxial layerand the mask pattern, and a sidewall of the pad pattern is laterallyrecessed from a sidewall of the mask pattern; forming a firstsemiconductor layer on the second epitaxial layer, wherein a sidewall ofthe mask pattern is covered by the first semiconductor layer, the firstsemiconductor layer extends to a space between the mask pattern and thesecond epitaxial layer, and a topmost end of the first semiconductorlayer is lower than a top surface of the mask pattern; removing the maskpattern, to expose an inner sidewall of the first semiconductor layerand a top surface of the pad pattern; removing a central portion of thepad pattern, to expose a portion of the second epitaxial layer; andforming a second semiconductor layer on the exposed portion of thesecond epitaxial layer.

In some embodiments, a method for forming the first semiconductor layercomprises: forming a semiconductor material layer on the secondepitaxial layer, wherein the mask pattern is covered by thesemiconductor material layer; and performing an etch back process on thesemiconductor material layer, to form the first semiconductor layer.

In some embodiments, the manufacturing method further comprising:forming an insulating layer covering the inner sidewall of the firstsemiconductor layer and the top surface of the pad pattern after removalof the mask pattern; forming a sidewall spacer on the insulating layer,wherein the inner sidewall of the first semiconductor layer and aperipheral portion of the pad pattern are covered by the sidewallspacer; removing a portion of the insulating layer by using the sidewallspacer as a shadow mask, so as to expose the central portion of the padpattern; and removing the sidewall spacer before removal of the centralportion of the pad pattern.

In some embodiments, the central portion of the pad pattern is removedby an isotropic etching process.

As above, the semiconductor device of the present disclosure may be aHBT device, and includes an epitaxial layer as a base, a semiconductorlayer as a contact layer of the base, and another semiconductor layer asan emitter. The emitter extends to the base from above the base, and avertically extending region of the emitter has a body portion and anextending portion extending from a bottom end of the body portion to atop surface of the base. The base contact layer laterally surrounds thevertically extending region, and further extends to a recess definedbetween the body portion of the emitter and the base. As a result, acontact area between the base contact layer and the base is increased,and a contact resistance between the base contact layer and the base isreduced. Such contact resistance is in negative correlation to anoperation frequency of the semiconductor device. Therefore, reduction ofsuch contact resistance may allow the semiconductor device to beoperated under higher frequency.

To make the aforementioned more comprehensible, several embodimentsaccompanied with drawings are described in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate exemplaryembodiments of the disclosure and, together with the description, serveto explain the principles of the disclosure.

FIG. 1 is a flow diagram illustrating a manufacturing method of asemiconductor device according to some embodiments of the presentdisclosure.

FIG. 2A through FIG. 2P are schematic cross-sectional views illustratingstructures at various stages during the manufacturing process of thesemiconductor device as shown in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a flow diagram illustrating a manufacturing method of asemiconductor device according to some embodiments of the presentdisclosure. FIG. 2A through FIG. 2P are schematic cross-sectional viewsillustrating structures at various stages during the manufacturingprocess of the semiconductor device as shown in FIG. 1.

According to some embodiments of the present disclosure, thesemiconductor device is a bipolar junction transistor (BJT) device, suchas a heterojunction bipolar transistor (HBT) device. In someembodiments, the manufacturing method of the semiconductor deviceincludes the following steps.

Referring to FIG. 1 and FIG. 2A, step S100 is performed, and a wellregion 102 is formed in a substrate 100. In some embodiments, thesubstrate 100 is a semiconductor substrate or asemiconductor-on-insulator (SOI) substrate. A semiconductor material inthe semiconductor substrate or the SOI substrate may include anelemental semiconductor (e.g., Si, Ge or the like), a semiconductoralloy (e.g., SiGe), a compound semiconductor (e.g., group III-Vsemiconductor or the like) or so forth, and the semiconductor materialmay be doped with a first conductive type or a second conductive typecomplementary to (or opposite to) the first conductive type. Forinstance, the first conductive type may be N-type, while the secondconductive type may be P-type. The well region 102 extends into thesubstrate 100 from a top surface of the substrate 100. In someembodiments, a conductive type of the well region 102 is different fromthe conductive type of the substrate 100. For instance, the substrate100 has the first conductive type, while the well region 102 has thesecond conductive type. Since the well region 102 will be covered byother components in the following steps, the well region 102 is alsoreferred as a buried well. In addition, in some embodiments, the wellregion 102 is formed by performing an ion implantation process on thesubstrate 100.

Referring to FIG. 1 and FIG. 2B, step S102 is performed, and anepitaxial layer 104 is formed on the well region 102. In someembodiments, the epitaxial layer 104 may be functioned as a collector ofthe eventually formed HBT device, whereas the well region 102 may be aportion of a contact region for routing a base of the eventually formedHBT. In these embodiments, the epitaxial layer 104 and the well region102 have the same conductive type (e.g., the first conductive type). Inaddition, a doping concentration of the epitaxial layer 104 may be lessthan a doping concentration of the well region 102. Alternatively, thedoping concentration of the epitaxial layer 104 is substantiallyidentical to or greater than the doping concentration of the well region102. In some embodiments, the epitaxial layer 104 and the substrate 100are made of different materials. For instance, the material of thesubstrate 100 may include Si, while the material of the epitaxial layer104 may include SiC. However, those skilled in the art may select othersuitable materials for the substrate 100 and the epitaxial layer 104according to process requirements, the substrate 100 and the epitaxiallayer 104 do not have to be made of different materials.

Referring to FIG. 1 and FIG. 2C, step S104 is performed, and anisolation structure 106 and an isolation structure 108 are formed in thecurrent structure. The isolation structure 106 and the isolationstructure 108 define an active region of the eventually formed HBTdevice (i.e., a space between isolation structure 106 and the isolationstructure 108). It should be noted that, as shown in FIG. 2C, theisolation structure 106 and the isolation structure 108 appear as twoseparate structures. Nevertheless, top view patterns of the isolationstructure 106 and the isolation structure 108 (not shown) may actuallybe connected with each other, and laterally surround the afore-mentionedactive region. In some embodiments, the isolation structure 106 extendsfrom a surface of the epitaxial layer 104 into the substrate 100 throughthe well region 102. In these embodiments, the isolation structure 106may have an upper portion 106 a and a lower portion 106 b. The upperportion 106 a extends into the epitaxial layer 104 from a top surface ofthe epitaxial layer 104. In some embodiments, the upper portion 106 amay not penetrate through the epitaxial layer 104, such that a bottomend of the upper portion 106 a is higher than a bottom surface of theepitaxial layer 104. The lower portion 106 b may extend from the bottomend of the upper portion 106 a into the substrate 100 through the wellregion 102. In some embodiments, a width of the upper portion 106 a isgreater than a width of the lower portion 106 b. On the other hand, theisolation structure 108 may be structurally identical to the upperportion 106 a of the isolation structure 106, and extends into theepitaxial layer 104 from the top surface of the epitaxial layer 104. Theisolation structure 106 and the isolation structure 108 may respectivelybe formed by an insulating material. In certain embodiments, aconductive material or a semiconductor material (not shown) may befurther filled in the lower portion 106 b of the isolation structure106. In these certain embodiments, the conductive material or thesemiconductor material may be surrounded by the insulating material,such that a bottom surface and a sidewall of the conductive material orthe semiconductor material are covered by the insulating material.

Referring to FIG. 1 and FIG. 2D, step S106 is optionally performed, anda heavily doped region 110 and a heavily doped region 112 are formed inthe epitaxial layer 104. The heavily doped regions 110, 112 extenddownwardly from the top surface of the epitaxial layer 104 to the wellregion 102 through the epitaxial layer 104. In some embodiments, theheavily doped region 110 and the heavily doped region 112 may furtherextend into the well region 102. The heavily doped region 110 is locatedwithin the active region defined by the isolation structure 106 and theisolation structure 108, whereas the heavily doped region 112 may belocated outside the active region. In other words, the heavily dopedregion 110 may be located between the isolation structure 106 and theisolation structure 108, while the heavily doped region 112 may belocated aside the isolation structures 106, 108. The heavily dopedregion 110, the heavily doped region 112, the epitaxial layer 104 andthe well region 102 have the first conductive type, and a dopingconcentration of the heavily doped regions 110, 112 may be greater thanthe doping concentration of the epitaxial layer 104. The well region 102and the heavily doped region 112 may collectively be functioned as acontact region of the collector of the eventually formed HBT device. Inaddition, by disposing the heavily doped region 110, a profile of adepletion region between the collector and the subsequently formed basecan be adjusted. The heavily doped region 110 may be disposed when theHBT device is used in low-voltage applications. Alternatively, theheavily doped region 110 may be omitted when the HBT device is used inintermediate-voltage or high-voltage applications. In some embodiments,the heavily doped region 110 and the heavily doped region 112 are formedby using at least one ion implantation process.

Referring to FIG. 1 and FIG. 2E, step S108 is performed, and anepitaxial layer 114, a pad layer 116 and a mask layer 118 aresequentially formed. The epitaxial layer 114, the pad layer 116 and themask layer 118 may cover the structure shown in FIG. 2D, and lie overthe epitaxial layer 104, the isolation structure 106, the isolationstructure 108, the heavily doped region 110 and the heavily doped region112. The epitaxial layer 114 may have the second conductive type, andmay be functioned as a base of the eventually formed HBT device. In someembodiments, a material of the epitaxial layer 114 includes SiGe. Inthose embodiments where the isolation structure 106 and the isolationstructure 108 are formed, portions 114 p of the epitaxial layer 114overlapped with the isolation structures 106, 108 may have apoly-crystalline phase, while other portions 114 m of the epitaxiallayer 114 overlapped with the epitaxial layer 104, the heavily dopedregion 110 and the heavily doped region 112 may have asingle-crystalline phase. In certain cases, interfaces between thepoly-crystalline portions 114 p and the single-crystalline portions 114m (depicted as dash lines in FIG. 2E) may extend obliquely, but thepresent disclosure is not limited thereto. On the other hand, the padlayer 116 and the mask layer 118 are formed on the epitaxial layer 114,and the pad layer 116 is located between the epitaxial layer 114 and themask layer 118. The pad layer 116 may have a sufficient etchingselectivity with respect to the mask layer 118, in order to prevent fromdamaging one of the pad layer 116 and the mask layer 118 while etchingthe other. In some embodiments, a material of the pad layer 116 includessilicon oxide, while the mask layer 118 is made of silicon nitride. Inaddition, in some embodiments, the mask layer 118 may have a thicknessgreater than a thickness of the pad layer 116. For instance, a ratio ofthe thickness of the mask layer 118 with respect to the thickness of thepad layer 116 may be greater than 7.

Referring to FIG. 1 and FIG. 2F, step S110 is performed, and the padlayer 116 as well as the mask layer 118 are patterned. The patterned padlayer 116 (referred as a pad pattern 116′ hereinafter) and the patternedmask layer 118 (referred as a mask pattern 118′ hereinafter) may beoverlapped with the heavily doped region 110 formed in the epitaxiallayer 104. In some embodiments, a patterning process for forming themask pattern 118′ is followed by a patterning process for forming thepad pattern 116′. In these embodiments, a photoresist pattern (notshown) may be initially formed on the mask layer 118, and then portionsof the mask layer 118 are removed by an anisotropic etching process viausing this photoresist patterns as a shadow mask, so as to form the maskpattern 118′. Subsequently, portions of the pad layer 116 are removed byusing the mask pattern 118′ as a shadow mask, so as to form the padpattern 116′. During patterning of the pad layer 116, an isotropicetching process may be used, such that an etchant may laterally etch aportion of the pad layer 116 lying under a peripheral portion of themask pattern 118′. Consequently, the formed pad pattern 116′ may belaterally recessed from a sidewall of the mask pattern 118′. In otherwords, the peripheral portion of the mask pattern 118′ may not beoverlapped with the pad pattern 116′. Accordingly, the subsequentlyformed semiconductor layer 120 (as shown in FIG. 2G) may extend into therecess defined below the peripheral portion of the mask pattern 118′.

Referring to FIG. 1 and FIG. 2G, step S112 is performed, and asemiconductor layer 120 is formed. The semiconductor layer 120 mayconformally cover substantially the entire structure shown in FIG. 2F.In other words, the epitaxial layer 114 and the mask pattern 118′ arecurrently covered by the semiconductor layer 120. In addition, anextending portion 120 a of the semiconductor layer 120 may furtherextend to the recess below the peripheral portion of the mask pattern118′. In some embodiments, the semiconductor layer 120 is in lateralcontact with the pad pattern 116′. In alternative embodiments, thesemiconductor layer 120 does not reach to the pad pattern 116′. Thesemiconductor layer 120 is made of a semiconductor material, and has thesecond conductive type. In some embodiments, a doping concentration ofthe semiconductor layer 120 is greater than a doping concentration ofthe base (i.e., the epitaxial layer 114), and may be functioned as acontact layer of the base (i.e., the epitaxial layer 114). In someembodiments, a material of the semiconductor layer 120 includespolysilicon. As described above, since the semiconductor layer 120 maylaterally extend into the recess below the peripheral portion of themask pattern 118′, a contact area between the semiconductor layer 120and the epitaxial layer 114 can be increased, and a contact resistancebetween the semiconductor layer 120 and the epitaxial layer 114 can beaccordingly reduced.

Referring to FIG. 1 and FIG. 2H, step S114 is performed, and an etchback process is performed on the semiconductor layer 120. In someembodiments, the etch back process ends when a topmost end of thesemiconductor layer 120 is lower than a top surface of the mask pattern118′. After performing the etch back process, the top surface and aportion of a sidewall of the mask pattern 118′ are exposed, and the maskpattern 118′ protrudes from the topmost end of the semiconductor layer120. In addition, the semiconductor layer 120 may be thinned during theetch back process. Those skilled in the art may adjust process time ofthe etch back process, in order to modify a shape of the semiconductorlayer 120. The present disclosure is not limited to a specific shape ofthe semiconductor layer 120, as long as the topmost end of thesemiconductor layer 120 is lower than the top surface of the maskpattern 118′.

Referring to FIG. 1 and FIG. 2I, step S116 is performed, and adielectric layer 122 is formed on the current structure. In someembodiments, the dielectric layer 122 globally covers the structureshown in FIG. 2H. In other words, a top surface of the semiconductorlayer 120, the top surface of the mask pattern 118′ and the previouslyexposed portion of the sidewall of the mask pattern 118′ are covered bythe dielectric layer 122. A material of the dielectric layer 122 mayinclude silicon oxide, silicon nitride, silicon oxynitride, the like orcombinations thereof.

Referring to FIG. 1 and FIG. 2J, step S118 is performed, and aplanarization process is performed on the dielectric layer 122. Duringthe planarization process, a top portion of the dielectric layer 122 maybe removed, such that the top surface of the mask pattern 118′ can beexposed. On the other hand, the top surface of the semiconductor layer120 as well as a top portion of the sidewall of the mask pattern 118′are still covered by the dielectric layer 122. In some embodiments, atop surface of the planarized dielectric layer 122 is substantiallycoplanar with the top surface of the mask pattern 118′. For instance,the planarization process may include a chemical mechanical polishingprocess, an etching process or a combination thereof. Since the topmostend of the semiconductor layer 120 is lower than the top surface of themask pattern 118′ as a consequence of the etch back process, the topmostend of the semiconductor layer 120 can be covered by the dielectriclayer 122, and the semiconductor layer 120 can be avoided from being indirect contact with the subsequently formed emitter.

Referring to FIG. 1 and FIG. 2K, step S120 is performed, and the maskpattern 118′ is removed. As a result, a recess RS is formed in thecurrent structure, and a top surface of the pad pattern 116′, a topsurface of the extending portion 120 a of the semiconductor layer 120,an inner sidewall of another portion of the semiconductor layer 120 andan inner sidewall of a portion of the dielectric layer 122 are exposed.The recess RS may be filled by the subsequently formed emitter. In someembodiments, the mask pattern 118′ may be removed by an etching process.For instance, this etching process may be an isotropic etching processor an anisotropic etching process.

Referring to FIG. 1 and FIG. 2L, step S122 is performed, and aninsulating layer 124 and a sidewall spacer 126 are sequentially formedon the current structure. The insulating layer 124 conformally coverssubstantially the entire structure shown in FIG. 2K, and may be made ofan insulating material (e.g., silicon nitride). In the eventually formedHBT device (as shown in FIG. 2P), the semiconductor layer 120 can beelectrically isolated from the subsequently formed emitter by theinsulating layer 124. On the other hand, the sidewall spacer 126 isformed in the recess RS, and covers a sidewall of the recess RS.Although the sidewall spacer 126 is depicted in FIG. 2L as two separateportions, the sidewall spacer 126 may continuously extend on an innerside of the recess RS. The sidewall spacer 126 may be functioned as ashadow mask in a subsequent step, and an opening surrounded by thesidewall spacer 126 defines portions of the insulating layer 124 and thepad pattern 116′ to be removed. In some embodiments, the sidewall spacer126 covers a portion of a bottom surface of the recess RS, but at leasta portion of the pad pattern 116′ is not covered by the sidewall spacer126. As shown in FIG. 2L, the sidewall spacer 126 covers the extendingportion 120 a of the semiconductor layer 120 and a peripheral portion ofthe pad pattern 116′, but a central portion of the pad pattern 116′ isnot covered by the sidewall spacer 126. In some embodiments, thesidewall spacer 126 may be made of a semiconductor material (e.g.,polysilicon). In addition, in some embodiments, a method for forming thesidewall spacer 126 includes globally forming a sidewall spacer materiallayer (not shown) on the insulating layer 124. Subsequently, a portionof the sidewall spacer material layer above the top surface of thedielectric layer 122 and a portion of the sidewall spacer material layerwithin a central region of the recess RS are removed by, for example, ananisotropic etching process, so as to form the sidewall spacer 126 asshown in FIG. 2L.

Referring to FIG. 1 and FIG. 2M, step S124 is performed, and exposedportions of the insulating layer 124 are removed by using the sidewallspacer 126 as a shadow mask. As shown in FIG. 2L and FIG. 2M, a portionof the insulating layer 124 above the top surface of the dielectriclayer 122 and another portion of the insulating layer 124 surrounded bythe sidewall spacer 126 are removed, and the top surface of thedielectric layer 122 and the central portion of the pad pattern 116′ areexposed. As shown in FIG. 2M, cross-sectional view of the remainedportion of the insulating layer 124 appears as two separate L-shapepatterns. In addition, a top end of the sidewall spacer 126 may behigher than a top surface of the dielectric layer 122 and a top end ofthe remained portion of the insulating layer 124. In some embodiments,an etching process (e.g., an anisotropic etching process) may be usedfor removing the fore-mentioned portions of the insulating layer 124.

Referring to FIG. 1 and FIG. 2N, step S126 is performed, and thesidewall spacer 126 and the exposed portion of the pad pattern 116′ areremoved. The remained portion of the insulating layer 124 is exposedonce the sidewall spacer 126 is removed. In some embodiments, an etchingprocess (e.g., an isotropic etching process) may be used for removingthe sidewall spacer 126. After the removal of the sidewall spacer 126, aportion of the pad pattern 116′ not covered by the insulating layer 124may be removed by another etching process, and a portion of theunderlying epitaxial layer 114 is accordingly exposed. In this way, thebase (i.e., the epitaxial layer 114) can be in contact with thesubsequently formed emitter. In some embodiments, the etching processfor removing the afore-mentioned portion of the pad pattern 116′ is anisotropic etching process (e.g., a wet etching process). In theseembodiments, since the pad pattern 116′ may have sufficient etchingselectivity with respect to the epitaxial layer 114, the epitaxial layer114 may be avoided from subjecting to damages during the etching processof the pad pattern 116′. In certain embodiments, the exposed portion ofthe epitaxial layer 114 has a substantially flat top surface.

Referring to FIG. 1 and FIG. 2O, step S128 is performed, and asemiconductor layer 128 is formed. In some embodiments, thesemiconductor layer 128 may be globally formed on the structure shown inFIG. 2N, and the recess RS may be filled by the semiconductor layer 128.In other words, the top surface of the dielectric layer 122, a surfaceof the insulating layer 124 and a sidewall of the pad pattern 116′ maybe covered by the semiconductor layer 128, and the semiconductor layer128 is in contact with a portion of the epitaxial layer 114. In someembodiments, a top surface of the semiconductor layer 128 has a recessRS' corresponding to the recess RS (as shown in FIG. 2M). Thesemiconductor layer 128 may be made of a semiconductor material with thefirst conductive type, and may be functioned as an emitter of theeventually formed HBT device. The semiconductor material of the emitter(i.e., the semiconductor layer 128) may be different from thesemiconductor material of the base (i.e., the epitaxial layer 114), thusa heterojunction is formed between the emitter and the base. Forinstance, a material of the semiconductor layer 128 may includepolysilicon, and a material of the epitaxial layer 114 may include SiGe.In addition, along a vertical direction, the semiconductor layer 128 maybe electrically isolated from the semiconductor layer 120 by thedielectric layer 122. On the other hand, along a lateral direction, thesemiconductor layer 128 may be electrically isolated from thesemiconductor layer 120 by the insulating layer 124 and the pad pattern116′.

Referring to FIG. 1 and FIG. 2P, step S130 is performed, and theepitaxial layer 114, the semiconductor layer 120, the dielectric layer122 and the semiconductor layer 128 are patterned. The patternedepitaxial layer 114, semiconductor layer 120, dielectric layer 122 andsemiconductor layer 128 may be overlapped with the active region definedby the isolation structures 106, 108, and the heavily doped region 112outside the active region may be currently exposed. In some embodiments,a lithography process and one or more etching process may be used forpatterning the semiconductor layer 128 and the dielectric layer 122.Subsequently, another lithography process and at least one etchingprocess may be used for patterning the semiconductor layer 120 and theepitaxial layer 114. In these embodiments, the patterned semiconductorlayer 128 and dielectric layer 114 may have a first footprint area, andspread within a span of the active region defined by the isolationstructures 106, 108. On the other hand, the patterned semiconductorlayer 120 and epitaxial layer 114 may have a second footprint area. Thesecond footprint area may be greater than the first footprint area, suchthat a portion of the semiconductor layer 120 is not covered by thedielectric layer 122 and the semiconductor layer 128. In addition, thepatterned semiconductor layer 120 and epitaxial layer 114 may be atleast partially overlapped with the isolation structures 106, 108.Alternatively, the patterned semiconductor layer 120 and epitaxial layer114 may not be overlapped with the isolation structures 106, 108.

In some embodiments, metal silicide layers 130 may be formed on exposedsurfaces of the semiconductor layer 128, the semiconductor layer 120 andthe epitaxial layer 104. For instance, a material of the metal silicidelayer 130 may include CoSi, TiSi, NiSi, the like or combinationsthereof. In those embodiments where the semiconductor layer 128, thesemiconductor layer 120 and the epitaxial layer 104 are made ofsilicon-containing material(s), exposed portions of the semiconductorlayer 128, the semiconductor layer 120 and the epitaxial layer 104 mayreact with metal elements during a thermal treatment, and the metalsilicide is accordingly formed. However, those skilled in the art mayselect other viable method for forming the metal silicide layer 130according to process requirements, the present disclosure is not limitedthereto.

Up to here, a HBT device 10 has been formed. As shown in FIG. 2P, theHBT device 10 may be a mesa-type HBT device. In other words, at leastsome portion of the HBT device 10 are formed on the substrate 100, andthese portions may be formed as a stacking structure with a mesaportion. The well region 102 and the epitaxial layer 104 (or the wellregion 102, the epitaxial layer 104 and the heavily doped region 110)may collectively be functioned as the collector of the HBT device 10,and have the first conductive type. The heavily doped region 112 formedin the epitaxial layer 104 may be functioned as a contact region of thecollector, and also has the first conductive type. In addition, theepitaxial layer 114 may be functioned as the base of the HBT device 10,and has the second conductive type. The semiconductor layer 120 formedon the epitaxial layer 114 also has the second conductive type, and maybe functioned as a contact layer of the base (i.e., the epitaxial layer114). Moreover, the semiconductor layer 128, which extends through thesemiconductor layer 120 and is in contact with the epitaxial layer 114(the base), may be functioned as the emitter of the HBT device 10, andhas the first conductive type. A vertically extending portion of thesemiconductor layer 128 is surrounded by the semiconductor layer 120,and can be regarded as having a body portion 128 b and an extendingportion 128 e extending downwardly from the body portion 128 b to a topsurface of the epitaxial layer 114. The body portion 128 b has a widthgreater than a width of the extending portion 128 e, and a portion ofthe semiconductor layer 120 (i.e., the extending portion 120 a of thesemiconductor layer 120) extends between the body portion 128 b of thesemiconductor layer 128 and the epitaxial layer 114. Therefore, acontact area between the semiconductor layer 120 and the epitaxial layer114 is increased, and a contact resistance between the semiconductorlayer 120 and the epitaxial layer 114 is reduced. Such contactresistance is in negative correlation to an operation frequency of theHBT device 10. In other words, reduction of such contact resistance mayallow the HBT device 10 to be operated under higher frequency. On theother hand, the extending portion 120 a of the semiconductor layer 120may be electrically isolated form the semiconductor layer 128 by theinsulating layer 124 and the pad pattern 116′.

Although not shown, other semiconductor devices may be formed in/on thesubstrate 100 along with the HBT device 10, and interconnectionstructures may be formed above the HBT device 10 and these semiconductordevices. For instance, these semiconductor devices may includehomogeneous BJT device(s), metal-oxide-semiconductor (MOS) field effecttransistor(s), the like or combinations thereof.

As above, the semiconductor device of the present disclosure may be aHBT device, and includes an epitaxial layer as a base, a semiconductorlayer as a contact layer of the base, and another semiconductor layer asan emitter. The emitter extends to the base from above the base, and avertically extending region of the emitter has a body portion and anextending portion extending from a bottom end of the body portion to atop surface of the base. The base contact layer laterally surrounds thevertically extending region, and further extends to a recess definedbetween the body portion of the emitter and the base. As a result, acontact area between the base contact layer and the base is increased,and a contact resistance between the base contact layer and the base isreduced. Such contact resistance is in negative correlation to anoperation frequency of the semiconductor device. Therefore, reduction ofsuch contact resistance may allow the semiconductor device to beoperated under higher frequency.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodimentswithout departing from the scope or spirit of the disclosure. In view ofthe foregoing, it is intended that the disclosure covers modificationsand variations provided that they fall within the scope of the followingclaims and their equivalents.

What is claimed is:
 1. A manufacturing method of a semiconductor device,comprising: sequentially forming a first epitaxial layer and a secondepitaxial layer on a substrate; forming a pad pattern and a mask patternon the second epitaxial layer, wherein the pad pattern is locatedbetween the second epitaxial layer and the mask pattern, and a sidewallof the pad pattern is laterally recessed from a sidewall of the maskpattern; forming a first semiconductor layer on the second epitaxiallayer, wherein a sidewall of the mask pattern is covered by the firstsemiconductor layer, the first semiconductor layer extends to a spacebetween the mask pattern and the second epitaxial layer, and a topmostend of the first semiconductor layer is lower than a top surface of themask pattern; removing the mask pattern, to expose an inner sidewall ofthe first semiconductor layer and a top surface of the pad pattern;removing a central portion of the pad pattern, to expose a portion ofthe second epitaxial layer; and forming a second semiconductor layer onthe exposed portion of the second epitaxial layer.
 2. The manufacturingmethod of the semiconductor device according to claim 1, wherein amethod for forming the first semiconductor layer comprises: forming asemiconductor material layer on the second epitaxial layer, wherein themask pattern is covered by the semiconductor material layer; andperforming an etch back process on the semiconductor material layer, toform the first semiconductor layer.
 3. The manufacturing method of thesemiconductor device according to claim 1, further comprising: formingan insulating layer covering the inner sidewall of the firstsemiconductor layer and the top surface of the pad pattern after removalof the mask pattern; forming a sidewall spacer on the insulating layer,wherein the inner sidewall of the first semiconductor layer and aperipheral portion of the pad pattern are covered by the sidewallspacer; removing a portion of the insulating layer by using the sidewallspacer as a shadow mask, so as to expose the central portion of the padpattern; and removing the sidewall spacer before removal of the centralportion of the pad pattern.
 4. The manufacturing method of thesemiconductor device according to claim 1, wherein the central portionof the pad pattern is removed by an isotropic etching process.